Crime Matthew Coleman, Accused of Killing Kids Over QAnon Theories, Is Undergoing Psychological Evaluation in Jail Matthew Taylor Coleman, 40, is charged with killing his 2-year-old son and 10-month-old daughter in Mexico on Aug. 9 By Steve Helling Published on August 26, 2021 05:18 PM Share Tweet Pin Email Trending Videos Matthew Taylor Coleman. Photo: Instagram Matthew Taylor Coleman is being held at an undisclosed federal prison after his arrest for allegedly killing his two children in Mexico -- and PEOPLE has learned that he will undergo psychological testing to determine his state of mind. Coleman is being held in protective custody. He has been charged with two counts of foreign murder of United States nationals. A law enforcement source tells PEOPLE in its upcoming issue that the next step is for Coleman to be assessed by a psychiatrist to determine whether he is fit to stand trial. Police say Coleman, a 40-year-old surfing instructor, drove the children -- 2-year-old Kaleo and 10-month-old Roxy -- into Mexico. Two days later, authorities allege, he took the kids to a ranch, where he killed them with a spearfishing gun and returned to his hotel a few hours later. He was arrested when he attempted to cross the border back into the United States. Calif. Surfing Coach Accused of Stabbing Children to Death in Mexico Is Arrested Trying to Return to U.S. For more on the disturbing case of Matthew Taylor Coleman, subscribe now to PEOPLE or pick up this week's issue, on newsstands Friday. According to charging documents, Coleman allegedly told police he was motivated by the QAnon conspiracy theory, which holds the false belief that former president Donald Trump has secretly been battling a cabal of Satan-worshipping pedophiles at the highest levels of political power and influence. PEOPLE obtained a criminal complaint that was filed in the U.S. District Court last Wednesday. In the 10-page complaint, FBI special agent Jennifer Bannon wrote that Coleman claimed to be "enlightened by QAnon and Illuminati conspiracy theories and was receiving visions and signs revealing that his wife, A.C., possessed serpent DNA and had passed it on to his children." "M. Coleman stated that he believed his children were going to grow into monsters so he had to kill them," Bannon wrote. Matthew Coleman, Abby Coleman. The sudden violence has shocked and saddened those who knew him, including his wife. "Abby is devastated," a family friend tells PEOPLE in its latest issue, on stands this week. "She is confused, stunned and just destroyed inside. She never had any idea he thought all these things. She thinks he just snapped. Something must have happened in his brain." It's unclear when the psychological assessment will be conducted -- or whether the results will be publicly released. Coleman has not yet entered a plea. The public defender's office has not returned PEOPLE's calls for comment.